1. Field of the Invention
The present invention is related to devices for restricting the flow of aspirant during surgery, especially ophthalmic surgery. In particular, the present invention relates to devices that are adjustable so as to provide a range of aspirant flow resistance and are incorporated into a surgical fluid collection cassette.
2. Description of Related Art
During eye surgery, especially cataract surgery, surgeons experience a tension between the amount of vacuum or aspiration to be used on a patient""s eye and the time period in which the surgeon has to respond to events that may occur during surgery. Surgeons typically prefer higher vacuum levels to provide a higher holding force for the cataract. However, these higher vacuum levels result in the need for rapid response times by the surgeon when events such as occlusion occur in the aspiration line. The higher the vacuum levels, the quicker events occur and thus the potential for serious problems increases, such as the tearing of the capsular bag.
There are known devices for increasing the resistance to aspirant fluid flow to allow a surgeon to use higher vacuum levels, i.e., higher holding force, with a slower response time. These devices help the surgeon have the benefits of higher vacuum levels while limiting or minimizing the risks by providing the surgeon with greater time to respond to surgical events than would be possible without resistance to the aspirant flow. Coiled tubing is one example that increases the flow resistance. It has been asserted that increased resistance is achieved by passing fluid through a series of coil bends because fluid drops in pressure as it flows through a bend. However, a downside to the coiled tubing is that the chances of aspirant clogging within the coils is increased due to the elliptical cross-section and bent kinks that may occur in the tubing. In addition, the resistance of the coiled tubing is a function of the coil radius and the resistance cannot be varied during surgery.
Another device that increases resistance to aspirant flow is a non-clogging orifice that collects waste and is commonly referred to phaco-guard. The phaco-guard is a large cross-sectional area filter funneled down to a small orifice. It allows limited clogging of the filter and is based on the assumption that the entire filter area will not clog. The filter may still clog and it is not adjustable.
Therefore, it would be advantageous to have a fluid flow resistor that is adjustable to provide the surgeon with a range of aspirant flow resistance.
It would be further advantageous to incorporate the fluid flow resistor into a aspirant fluid collection cassette to reduce the number of devices needed by a surgeon, and also to easily allow automation or motorization of the resistance adjustment.